Three dimensional positioning device

ABSTRACT

A three dimensional positional device which may be used with a computer to enable, for example, a cursor to be moved in three dimensions. The device includes a movable portion ( 64 ) and a stationary portion ( 61 ). Movement of the movable portion ( 64 ) is translated into the movement of three Hall effect devices ( 69, 77, 81 ) in three orthogonal directions, relative to three magnetic systems ( 67, 72, 82 ). The movable portion ( 64 ) may be moved in a plane and pivoted relative to the stationary portion ( 61 ).

The present invention relates to a positional device which will providethree electrical signals proportional to the movement of a portion ofthe device in three dimensional space, i.e. proportional to the threecoordinate axes x, y and z defining that position, and particularlyalthough not exclusively to a device for use in conjunction with acomputer to enable the movement of a cursor or object in the x-y and zdirections as represented on a computer monitor.

Conventional arrangements used with computers to locate the preciseposition of a cursor on a screen (as in the Xerox Corporation “mouse”)are capable only of providing a signal relating to movement in twodimensions. It is known that existing mouse type positioning devices andalso similar two dimensional positioning devices such as touch screens,light pens, etc. are often inaccurate, difficult to use, ergonomicallytiring, often restrictive in use and particularly in the case of themouse, prone to degradation through the accumulation of dust and dirt.

Existing positional devices for computers are known, where a signalrelating to position is determined by the interaction of a Hall effectdevice with a magnetic field. Hall devices are a known method ofdetermining magnetic field strength, they depend on the interaction of amagnetic field on the current carried in a conductive material,typically a thin layer of a semiconductor. We refer to the Hall effect,first discovered by E. H. Hall in 1878 and the technology subsequentlyrefined since then.

The principal features of the Hall effect are that the incidence of amagnetic field (B-field) on a current carrying conductor yields a Hallvoltage, proportional to B. This Hall voltage is a maximum when theB-field and conductor surface are orthogonal.

Now, any magnetic field exists in three dimensions and a system of Halldevices located near a point in magnetic space will give Hall voltageswhich are a unique function of that point in magnetic space. If a systemof magnets are used to develop a particular spatial magnetic fieldconfiguration and this system is mobile, relative to a system of Hallprobes, then the Hall voltages generated in these Hall devices will,after processing, define the position of the magnetic system.

A number of patent applications have utilised this approach, inparticular the following:

U.S. Pat. No. 4,459,578 Jul. 10, 1984

U.S. Pat. No. 4,639,667 Jan. 21, 1987

U.S. Pat. No. 4,654,576 Mar. 31, 1987

U.S. Pat. No. 4,825,157 Apr. 25, 1989

A disadvantage with this approach is the looseness, ambiguity and lackof precision of the geometric centre of such a magnetic assembly. Otherdisadvantages are the smallness of the B-field, the difficulty of fluxconcentration and that the movement of magnets generates circulatingcurrents in the magnetic material creating additional fieldssuperimposed on the main ones. A practical disadvantage is that such amagnetic sensor is often large and very bulky. The use of large magnetsmay also necessitate the use of shielding to prevent the magnetic fieldgenerated from interfering with magnetically sensitive equipment.

Another existing arrangement is described in WO 93/20535. Thisarrangement takes the form of a joystick and comprises a body includingan end wall in which is secured a resilient arm. The resilient arm hassecured to its top a tube and a handle. The tube surrounds the arm andmounts an annular magnet at the level of a pivot point, about which thearm flexes. The outputs of four Hall effect probes are affected by theposition of the magnet to give an indication of the position of the arm,in two dimensions. The angular position of a, second, rotary handle issensed by way of a further magnet which is connected for movement withthe handle relative to further Hall effect probes.

Another use of a Hall effect device is disclosed in U.S. Pat. No.5,004,871 which describes a stylus of a type suitable for use with acomputer. The stylus has a pressure sensitive switch which may comprisea magnet and a Hall effect device mounted for movement relative to eachother.

There are also a number of existing three dimensional positional devicesavailable, for use in conjunction with computers. These devices use avariety of methods for generating a signal which relates to movement inthree dimensions, including the use of gyroscopic systems to determinethe movement of a device in space, electro-optical systems and in onedevice the use of strain gauges to determine the movement of a portionof the device relative to the remainder of the device. Existing threedimensional positional devices are expensive and/or imprecise, awkwardand tiring to use, and in some cases physical constraints limit the useof the device.

An object of the present invention is to provide a three dimensionalpositional device which is convenient, simple and accurate and will,when used as an input device for a computer, enhance the capabilities ofexisting and future software technology and allow the exploitation ofnew more powerful computers.

Additional devices are foreseen for use with computer games, medical,computer graphics, virtual reality, robotics, security, teaching andother consumer and industrial applications.

According to a first aspect of the present invention there is provided athree dimensional positioning device comprising three Hall effectdevices mounted on movable supports and three associated means forproducing a magnetic field mounted on stationary supports adjacent butdisplaced from the movable supports.

Preferably the three magnetic systems are unconnected and unrelated. Themagnetic systems each preferably comprise two magnets arranged inrepelling mode polarity and the Hall effect devices are arranged to movebetween the opposed magnets. In this arrangement the Hall voltagemeasured will correspond to the position of the device between the twomagnets, being a positive maximum when the Hall device is adjacent toone of the magnets and a negative maximum when the device is adjacent tothe opposite magnet. The magnets preferably comprise small Nd.B.Fe RareEarth magnets of high coercivity although they could comprise any othersuitable magnetic material. The Hall devices are preferably comprised ofconventional commercially available semiconductor Hall chips, althoughthey could be effected by highly sensitive two dimensional electron gas(2DEG) Hall devices.

The three Hall devices and associated magnets are preferably mounted ina body having the appearance of the familiar two dimensional positionaldevice, the mouse, but arranged to furnish three dimensional movementachieved by movement of the cover of the device with respect to itsbase. Movement of the three Hall devices may be proportional to thecomponents of the movement of the cover of the device with respect toits base in three orthogonal directions. Springs may be employed toreturn the Hall devices to predetermined positions relative to theirassociated magnets when no external forces are applied to the device.Preferably the distance between any of the three positional modules(each comprising two opposed magnets and an associated Hall device) isgreater than the distance between the opposed magnets of any one of themodules, more preferably the distance between any of the modules is atleast twice the distance between the opposed magnets of any one module.The Hall voltages are preferably measured using conventionalcommercially available electronics and encoded for onward transmissionto a computer by wire or by infra red or radio transmission, in whichcase the power supply for the device is preferably provided by means ofa rechargeable battery and means for recharging this battery is providedintegrally with the equipment that the positional device is intended foruse with. The encoded information relating to the three Hall voltages ispreferably processed by means of driver software which serves to move acursor or object on the computer monitor in response to the signalsreceived from the positional device, for example movement in twodimensions can be represented by movement of an object across thesurface of a two dimensional screen and movement in a third dimension bychanging the size of that object, although there are other possible waysthat movement in three dimensions can be represented. The way in whichthe object controlled by the mouse behaves in response to movement ofthe positional device is also governed by its driver software and can betailored to suit the application for which the positional device is tobe used. Preferably movement of the cover of the positional device in adirection, for example sliding the cover in the x direction, causes theobject controlled by the device to accelerate in that direction on thecomputer monitor and returning the device to the original position, orreleasing one's grip on the device, causes the object to stop moving.Also, the cover of the mouse type device preferably incorporatesbuttons, similar to the conventional two dimensional mouse, to provideadditional input to software and could also, for example, enable thedevice to be used for input of six degrees of freedom, i.e. movementalong and rotation about three orthogonal axes.

It will be appreciated, however, that other embodiments are possible,for example where a system of Hall effect devices are arranged, withappropriate mechanical linkages, in different device bodies. Examples ofother possible embodiments include a joystick, single handed device, twohanded or multi-user device and also location and motion detectors forindustrial use.

According to a second aspect of the present invention there is provideda three dimensional positional device comprising a stationary portionand a movable portion wherein movement in two dimensions is effected bymoving the movable portion in a plane relative to the stationary portionand movement in a third dimension is effected by pivoting the movableportion relative to the stationary portion.

Preferably, the axis about which the movable portion may be pivoted isparallel to the plane. Preferably, where movement of the movable portionin the plane is resolved into two axes, possibly for onwardtransmission, then the axis about which the movable portion may bepivoted is parallel to one of the two axes in the plane. Where movementin the plane is resolved into orthogonal axes, say x and y axes, thenthe movable portion may preferably be pivoted about an axis parallel toone of those axes, say the x-axis.

Where movement of the movable portion is encoded for onward transmissionto a computer, or other device, then it is preferable that movement ofthe movable portion in the plane represents movement in the x-y planeand pivoting of the movable portion represents movement in the zdirection, orthogonal to the x-y plane.

Movement of the movable portion relative to the stationary portion ispreferably measured by means of a magnetic system comprising a Halldevice or devices and means for producing a magnetic field, although anyother suitable means may be employed, for example switches or an opticalsystem. The Hall device or devices are preferably mounted on a movablesupport or supports and the means for producing a magnetic field mountedon a stationary support or supports, adjacent but displaced from themovable support(s). The movable supports are preferably linked to themovable portion of the device. The means for producing the magneticfield preferably comprises a permanent magnet or magnets, for examplesmall Nd—Be—Fe Rare Earth magnets.

Preferably there are provided three Hall effect devices, movablerelative to three unconnected and unrelated magnetic systems, ashereinbefore described. Two of the magnetic systems are preferablyarranged to measure movement of the movable portion in each of twoorthogonal directions in the plane and the third magnetic system theextent to which the movable portion is pivoted relative to thestationary portion.

In one embodiment two of the three Hall effect devices are mounted onslides, so arranged within the body of the positional device so thatmovement of the cover with respect to the base of the device results inthe movement of the Hall devices relative to their associated magnets.

The remaining Hall device is preferably mounted on a pivoting member,arranged to move with the movable portion of the device, and itsassociated magnets are mounted on the stationary member. The slides maybe connected directly to the movable portion, or by way of a connectingrod and pivot arrangement. A bearing or bearings may be disposed betweenthe movable and stationary positions, to facilitate their relativemovement. A resilient means, for example return springs may be disposedbetween the movable and stationary portions, to return the two portionsto a predetermined relative position when no external force is applied.

The device preferably has the appearance of a conventional ‘mouse’device, the movable portion being comprised in the cover and thestationary portion being comprised in the base. The device may bearranged so that the movable portion may be pivoted about more than oneaxis, to allow for the input of additional degrees of freedom.

The present invention affords a number of advantages over the prior art,the use of static magnets eliminates the generation of eddy currents innearby metallic members and hence additional magnetic fields generatedby those currents and consequent errors in signals produced by thedevice. The use of a magnetic system is advantageous over those priorart devices which employ mechanical means for determining position, asmagnet systems do not involve moving contacts they are unaffected by theaccumulation of dust and dirt.

A means to exclude dust and dirt, for example a flexible skirt, may bedisposed between the movable and stationary parts of the positionaldevice.

Where a device may be used to provide two dimensional movement throughsliding of a portion relative to another, and movement in a thirddimension by pivoting, this provides a less ergonomically tiringarrangement than many prior art devices. The user may rest their hand onthe device in use rather than having to raise or lower a portion of thedevice involving lifting their hand and arm. The provision of return tozero springs and more particularly variable rate return to zero springscan improve the feel of the device. Alternatively an actuator oractuators could be employed by counter movement of the device to giveadditional feed back to the user.

Referring, in particular, to the mouse type configuration, in use thisembodiment is static relative to its surroundings in contrast toexisting “mouse” positioning devices which are mobile, this reduces theincidence of repetitive strain injury resulting from use of the device.

The use of three similar positional modules within the device results ina system which is easy and cheap to assemble. The three positionalmodules are small relative to the body of the device, particularly thedistance between the two opposed magnets of each module is less than thedistance between the separate modules, this reduces magneticinterference between the three modules and also the generation ofexternal magnetic fields, this eliminates the need for shielding toprevent interference with outside, magnetically sensitive equipment.

In order that the invention be more clearly understood there are nowdescribed embodiments thereof, by way of example, with reference to theaccompanying drawings in which:

FIG. 1 shows a cutaway, perspective view of a first embodiment of athree dimensional mouse type positional device;

FIG. 2 shows a cross-sectional plan view of a second embodiment of athree dimensional mouse type positional device;

FIG. 3 shows a longitudinal cross-sectional view of a positional device,of the type illustrated in FIG. 2;

FIG. 4 shows a transverse cross-sectional view of a positional device,of the type illustrated in FIGS. 2 and 3;

FIG. 5 shows a partial cutaway schematic view of a third embodiment of athree dimensional mouse type positional device;

FIG. 6 shows a similar view to FIG. 5 with both x and y magnets shown;

FIG. 7 shows an exploded view of the positional device of FIGS. 5 and 6;

FIG. 8 shows a plan view of the ‘z’ chassis of the device of FIGS. 5 to7;

FIG. 9 shows a similar view to FIG. 8, where the thrust ball race hasbeen displaced from the central position;

FIG. 10 shows a schematic representation of the electrical connection ofthe three Hall effect devices used in a positional device; and

FIG. 11 shows an alternative implementation to the circuit arrangementillustrated in FIG. 10.

Referring to FIG. 1 there is illustrated a positional device. Forreference purposes and to aid clarity, there are also marked thedirections of three coordinate axes, x-y and z. The body of the deviceis comprised of a base 1 and a cover 2. At the interface between theperiphery of the base 1 and cover 2 there is provided sufficientclearance to allow the cover 2 to be moved a predetermined amount in thehorizontal (x-y) plane, and also to be pivoted about an axis parallel tothe x axis, relative to the base 1.

Attached to the cover 2 are two forked formations, the x-fork 3 and they-fork 4. Both the forks are comprised of three parallel prongs ofcircular cross-section. The prongs of the x-fork 3 are aligned along they-direction, the prongs of the y-fork 4 are aligned along thex-direction, as marked on the reference axes on the diagram. The x and ydirections are orthogonal. Attached to the end of the central prong ofeach forked member there is a Hall effect device. Attached to thecentral prong of the x-fork 3 is the x-Hall effect device 14, the x-Halldevice 14 is comprised of a conventional semiconductor Hall chip, formedfrom a substantially flat rectangular piece of semiconductor material,the plane of which is aligned approximately with the y,z plane.Similarly, there is attached a Hall effect device to the y-fork 4, thisy-Hall effect device 15 is similar to the x-Hall effect device 14although it is aligned approximately with the x,z plane.

The x-fork 3 and the y-fork 4 are engaged respectively with the x-slide13 and the y-slide 16.

Attached to the base 1, by means of a pivot 5, is a structure, thez-pivoting member 6, arranged to pivot about an axis parallel to thex-axis. Secured to a projecting portion of the z-pivoting member 6 isthe z-Hall probe 7. The z-Hall probe 7 is fixed relative to thez-pivoting member 6 and arranged to move between the two z-magnets 8,9one of which 8, is secured to the base 1. The second magnet 9 is securedto a projecting tab, formed into the base. The z-magnets are arranged inrepelling mode polarity, and comprise rare earth magnets, for exampleNd—B—Fe.

The base 1, cover 2, forks 3 and 4 and z-pivot are preferablyconstructed from a plastics material.

Located between the z-pivoting member 6 and base 1 are two z-returnsprings 10, they are arranged to move the z-pivoting member 6 to aposition where the z-hall probe 7 lies midway between the z-magnets 8and 9, when no external forces are applied to the system. Formed intothe z-pivoting member 6 are two recesses, the x-recess 11 and they-recess 12.

Referring to the x-recess 11, there is slidably mounted in this recessthe x-slide 13. The x-slide is able to slide in the y-direction,relative to the z-pivoting member 6.

Similarly there is provided a y-slide 16, slidably mounted into they-recess 12 and movable with respect to the z-pivoting member 6 in thex-direction.

The x and y-slides are provided with central apertures, magnets aresecured into the opposite ends of each aperture, arranged in repellingmode polarity. The x-magnets 17 are opposed along a line in thex-direction, the y-magnets 18 are opposed along a line in they-direction.

The x-fork 3 and the y-fork 4 extend into the x and y recesses 11,12formed through the z-pivoting member 6 and engage with the x-slide 13and y-slide 16 respectively.

Between the outer prongs of the x-fork 3 and side of the x-recess 11,there are disposed x-return springs 19, arranged to return the x-fork 3to a predetermined position in the x-recess 11, when no external forcesare applied, so that the y-Hall effect device 15 lies midway between thev-magnets 18.

Similarly y-return springs 20 are disposed between the y-fork 4 and they-recess 12, so as to return the x-Hall effect device 14 to amid-position between the x-magnets 17, when no external forces apply.

The return springs are constructed from Beryllium Copper, a nonmagneticmaterial.

Although not shown, the Hall effect devices are connected to a suitablepower supply which supplies a direct current. The Hall devices are alsoconnected to monitoring equipment able to monitor the Hall voltages todetermine the position of the Hall effect devices between theirassociated opposed magnets. The information regarding the position ofthe three Hall devices is conveyed to appropriate electronics, foronward transmission to a computer.

In use the cover of the device 2, is moved with respect to the base 1.If the cover 2 is slid in an x-direction relative to the base, theeffect is to move the x-Hall device 14 relative to the x-magnets 17.Similarly, sliding the cover relative to the base in a y-directionresults in movement of the y-Hall effect device 15 relative to they-magnets 18. Pivoting the cover 2 with respect to the base 1 results inthe pivoting of the z-pivoting member 6 and the movement of the z-Halleffect device 7 between the z-magnets 8 and 9.

This movement of the cover 2 with respect to the base is effective tomove three Hall effect devices in three orthogonal directions, theposition of the Hall effect devices enables an electrical signalrelating to movement in three dimensions to be generated. This would,for example with the use of appropriate driving software be able toallow the movement of an object or cursor in three perceived dimensionson a computer screen.

Referring to FIGS. 2, 3 and 4 there is illustrated an alternativeembodiment of the present invention, also having a cover 25 and a base26.

Attached to the base by means of a pivot 27 there is a pivoting member28.

Again, for clarity the drawings are marked with the three coordinate,x-y and z directions. The pivoting member is arranged to pivot about thex-axis.

The pivoting member 28 has affixed to one end thereof a Hall effectdevice 29, which moves between two opposed rare earth magnets 30. Thepivoting member 28 is supported by two springs 61, these springs serveto return the pivoting member 28 to a position where the Hall effectdevice 29 lies in a predetermined position between the magnets 30, whichare mounted, fixed, relative to the base 26. Attached to the pivotingmember are a second pair of magnets, the x-magnets 31. These magnets aremounted in formations produced from the same material as the pivotingmember 28 and arranged so as to be in repelling mode polarity. Themagnets 30 and 31 comprise rare earth magnets, for example Nd—B—Fe.

Slideably mounted to the pivoting member 28 there is the x-slide 32,arranged to be able to slide with respect to the pivoting member 28 inthe x-direction.

Forming part of the x-slide 32 there is an arm 33 to which there isattached a Hall device 34, movement of the x-slide 32 relative to thepivoting member 28 results in movement of the Hall device 34 relative tothe x-magnets 31.

Mounted on the x-slide 32 are two magnets 36, similar to magnets 31,also placed in repelling mode polarity. Also, there are provided tworeturn springs 37 bearing on both the x-slide 32 on pivoting member 28and arranged to move the x-slide 32 relative to the pivoting member, toa predetermined position when no external forces are applied to thedevice. Typically in order that the Hall effect device 34 lies midwaybetween x-magnets 31.

Further there is slidably mounted to the x-slide 32, a y-slide 35movable in the y-direction relative to the x-slide 32.

Projecting from the y-slide 35 there is an arm 38 to the end of whichthere is affixed the y-Hall effect device 39. The arm 38 is arranged inorder that the y-Hall effect device 39 moves between magnets 36 inresponse to movement of the y-slide 35, relative to the x-slide 32.Further, placed at opposite ends respectively of the y-slide 35 betweenthe y-slide 35 and projecting portions of the x-slide 32 are returnsprings 40, arranged to return the y-slide 35, when no external forcesare applied, to a predetermined rest position with respect to thex-slide 32. Typically, so as to return the y-Hall effect device 39 to amid-position between the y-magnets 36.

The uppermost part of the y-slide 35, labelled 41 is of a squarecross-section and has a projecting lip. The underside of the cover 25also has a projecting portion 42, which cooperates with the uppermostpart of the y-slide 41. This arrangement enables the cover to be fittedto the y-slide with a “snap-fit”, in order that movement of the coverresults in movement of the y-slide.

The device body and slides are constructed from a non-magnetic plasticsmaterial, the return springs are constructed from Beryllium Copper.

Movement of the cover 25 relative to the base 26, either by sliding thecover in the x-y plane or tilting the cover about an axis, parallel tothe x-axis, results in corresponding movements of the x-y and z-Halleffect devices relative to their associated magnets.

Referring to FIGS. 5 to 9 there is shown a further embodiment of apositional device according to the invention. This embodiment alsoincludes a base 61 and cover 64, the cover includes three buttons 74,the shape of the cover 64 is ergonomically designed to facilitatecomfortable operation with one hand. The opposite end of the cover 64 tothat which includes the switches provides a surface on which the usermay rest their wrist when using the device. In comparison with the otherembodiments described above, this embodiment includes a mechanicallinkage arranged to translate movement of the cover 64 with respect tothe base 61 into the movement of three Hall effect devices with respectto three pairs of stationary magnets. In this embodiment the cover 64 isconnected to a shaft 62. Mounted rotatably on the shaft are twoconnecting rods, the x-connecting rod 75 and the y-connecting rod 63.The connecting rods 75 and 63 are pivotally connected to the x and ypistons 76 and 66. The pistons are in turn connected to x and y Hallchip holders 77 and 69 respectively.

The pistons are slidably mounted in piston blocks 67 which include meansto enable two permanent magnets 68 to be mounted. The piston blocks 67constrain the pistons 66 and 76 and hence the Hall chip holders 69 and77 to move linearly between the magnets 68. The pistons 66 and 78 areillustrated as being circular in cross-section although they could takeany other suitable form.

Mounted at the opposite end of the shaft 62 to the cover 64 is a thrustring ball race 72. The thrust ring ball race 72 sits in an enclosedregion 71 formed by barrier 78 which is formed on the chassis 65. Thethrust ring ball race 72 is retained within raised portion 78 by ballrace cover 79 which engages with the barrier 78 with a snap-fit. Thethrust ring ball race 72 enables the cover 64 to move laterally withrespect to the base 61, by a limited amount. When the cover is so movedthe x and y pistons 76 and 66 respectively are moved in the x and ydirections by the x and y components of the motion of the cover.

Also mounted within the raised portion 78 are four return springs 73which act to centralise the thrust ball race 72 in the recess 71 when noforce is applied. When the thrust ball race 72 is centralised then, boththe x and y Hall chip holders 77 and 79 are aligned approximately midwaybetween their respective magnets.

An alternative return spring arrangement to that illustrated in FIG. 7is illustrated in FIGS. 8 and 9.

In the arrangement illustrated in FIG. 8 the return springs 73 aresupplemented by pressure bars 84. The springs 73 act to centralise thethrust ball race 72 within the area defined by raised portion 78, whenno pressure is applied, that is, a return to zero function. FIG. 9 showsa similar view to FIG. 8 but with the thrust ball race 72 displaced fromthe central position.

The ball race arrangement allows the cover 64 to be smoothly moved withrespect to the base 61. The return springs give the cover ‘feel’, inthat the user is required to move the cover against spring pressure toregister movement of a cursor on a computer screen, for example.

The return springs 73 may be variable rate springs, arranged to provideonly a low force against any initial movement, but to provide anincreased force when the ball thrust race 72 is displaced further.

The x and y piston blocks 67, recess 71 and ball thrust race 72 are allmounted on the z chassis 65.

The z chassis 65 is pivotally mounted onto the base 61 by engagingformations 79 and 80. A z-axis Hall chip holder 81 is also mounted ontothe z chassis 65 and a z magnet holder 82 for holding two opposedmagnets is mounted on base 61. Disposed between the z chassis 65 andbase 61 are four z-return springs 83 which serve to return the z-chassisto a position where the z Hall chip holder 81 lies approximatelyhalf-way between the two z magnets retained in the z-magnet holder 82,when no force is applied.

In a similar manner to the first and second described embodiments, themovement in the z-direction is effected by tilting the cover 64 withrespect to the base 61, about an axis parallel to the x-axis. Tiltingthe cover 64 causes the z-chassis to pivot with respect to the base,against the z-return springs 83, and hence move the z Hall chip holderand the Hall chip retained therein with respect to the stationarymagnets retained in the z-magnet holder 82.

Finally, there is also mounted on the base 61 a printed circuit board 84on which is mounted appropriate circuitry (not shown) for the operationof the three Hall chips and buttons.

Also attached to the circuit board 84 are three chip ribbons 85 forelectrical connection of the electronic circuit to the Hall chips.

All parts of the device, other than the magnets, are produced from anon-magnetic material, preferably a plastics material.

This embodiment provides a particularly smooth action, especially whenthe cover is moved in the z and y directions. Moreover the x and y chipsare constrained by the x and y pistons 76 and 66 respectively to move ina linear path between their respective magnets. This leads to moreaccurate operation of the device.

Referring to FIG. 10 there is a illustrated a representation of the Halldevice and magnet positional arrangements, for the x-y and z axes, asused in the foregoing embodiments of positional devices.

Referring to the x-axis arrangement 45 there is illustrated a Halleffect device 46 and two magnets arranged in repelling mode polarity 47and 48. The Hall effect device is able to move relative to and betweenthe magnets 47 and 48. As the magnets are arranged in repelling mode,the Hall voltage measured across the Hall effect device 46 will be amaximum when the Hall effect device approaches one of the magnets and anegative maximum when the second magnet is approached. The Hall voltagemeasured will vary approximately linearly as the device is moved betweenthe two magnets.

In use, each of the three Hall devices are connected to a power supply49 which supplies a direct current, for example a battery. In addition,each device is connected to an amplifier 50, which produces a signalrelating to the Hall voltage generated across the Hall effect devicewhich relates to the position of the device.

The three signals relating to the positions of the x-y and z-Hall effectdevices, relative to their corresponding magnets are supplied to amicroprocessor 51.

The microprocessor converts the three Hall voltages into a signalsuitable for processing by the driver software of a computer, whichconverts the position and movement of the Hall effect devices to theposition and movement of a cursor or object on the computer screen. Thebehaviour of the cursor or object on the computer screen in response tomovement of the cover of the position devices relative to its base isdetermined by the computer driver software. In the above embodiments thesoftware is arranged so as to cause the cursor or object to acceleratein a given direction in response to the movement of the cover of thedevice relative to the base, in that direction. When pressure isreleased on the cover the return springs act to return the Hall devicesto their predetermined rest position, which corresponds to a stationarycursor. This software enables the cursor to be rapidly moved to a pointon the screen, the body of the mouse is then released and more accuratepositioning of the cursor can then be achieved.

Referring to FIG. 11 there is illustrated an alternative arrangement forthe electrical connection of three Hall effect devices. The signals fromsensors 52 of the Hall effect device are fed to an amplifier 53 whoseoutput is connected via an analogue to digital converter 54 andmicrocontroller 55 to a transmitter 56. On the receiving side, areceiver 57 is connected via a microcontroller 58 and buffer 59 to acomputer 60.

In use both of the above embodiments are static relative to theirsurroundings. Use of the devices is achieved by the sliding and pivotingof the cover of the devices with respect to their bases. Thisarrangement is convenient to use and in comparison with existingpositioning devices, more accurate and less likely to cause repetitivestrain injury.

The above embodiments are described by way of example only, manyvariations are possible, without departing from the invention.

What is claimed is:
 1. A three dimensional positioning device comprisingthree Hall effect devices mounted on movable supports, and threeassociated means for producing a magnetic field mounted on stationarysupports adjacent but displaced from the movable supports wherein eachmeans for producing a magnetic field comprises two spaced apartpermanent magnets arranged in repelling mode polarity and eachassociated Hall device is constrained to move between two such magnets.2. The positional device of claim 1, wherein the three Hall effectdevices are movable in three orthogonal directions.
 3. The positionaldevice of claim 1, wherein at least one Hall effect device is mounted ona sliding member.
 4. An input device for a computer comprising: astationary portion; a movable portion mechanically connected to andmoveable relative to the stationary portion; and means for detectingrelative movement of the two portions and outputting a signal fortransmission to a computer, the output signal representing movement infirst, second and third orthogonal directions; wherein movement of themoveable portion is effected by sliding the movable portion in a planerelative to the stationary portion and by pivoting the movable portionrelative to the stationary portion, wherein the movable portion isconstructed and arranged to be pivoted about an axis which is parallelto the plane, and wherein movement of the moveable portion relative tothe stationary portion in the plane causes the device to output a signalrepresentative of movement in the first and second orthogonaldirections, and pivoting the moveable portion relative to the stationaryportion causes the device to output a signal representative of themovement in the third orthogonal direction.
 5. The positional device ofclaim 4, further comprising a Hall effect device and a means forproducing a magnetic field.
 6. The positional device of claim 5, whereinthe Hall effect device is mounted on the movable support and the meansfor producing a magnetic field is mounted on a stationary support,adjacent to and spaced apart from the movable support.
 7. The positionaldevice of claim 4, comprising three Hall effect devices and threeassociated means for producing a magnetic field.
 8. The positionaldevice of claim 7, wherein the three Hall effect devices are movable inthree orthogonal directions.
 9. A three dimensional positioning devicecomprising three Hall effect devices mounted on movable supports, andthree associated means for producing a magnetic field mounted onstationary supports adjacent to the movable supports wherein each meansfor producing a magnetic field comprises two spaced apart permanentmagnets arranged in repelling mode polarity and each associated Halldevice is constrained to move between two such magnets.